The invention concerns aliphatic diisocyanates; particularly decane-1,10-diisocyanates, with the alkyl chain capable of being diversely substituted in positions 1 and 10. These isocyanates are prepared by the phosgenation of the corresponding amines and are especially advantageous in the synthesis of polyurethanes used particularly in the preparation of non-yellowing varnishes and paint.
Two phosgenation techniques can be advantageously implemented in order to prepare such diisocyanates. One consists of causing the amine to react at low temperature with the phosgene in a solvent in order to form carbamoyl chloride, and then to raise the temperature in order to decompose the latter and recover the isocyanate. The other one consists of synthesizing the amine chlorhydrate, isolating it, and making it react in a temperature range of 120.degree. to 190.degree. C., with a current of gaseous phosgene.